1. Field of the Invention
The present invention relates to a motor-controlling circuit used for an optical-axis-adjusting unit of a vehicle illuminating device.
2. Description of the Related Art
A unit for controlling the irradiating direction, which adjusts the optical axis of a vehicle illuminating device in compliance with a change in the posture of the vehicle, has been known as a so-called leveling unit. For example, there is a unit by which the optical axis is manually adjusted by an operation switch in response to the riding conditions of passengers and/or cargo-loading conditions in a vehicle. Also, there is a unit by which the lighting or irradiating direction is automatically corrected so that the irradiating direction of an illuminating device can be kept constant in response to changes in the running conditions of a vehicle (a so-called auto-leveling unit).
As a mechanism for adjusting the optical axis (or correcting the optical axis), there has been known a mechanism in which the position and posture of the illuminating device or optical system components are changed by a direct current motor and its drive controlling circuit. For example, there is employed a construction in which an analog drive method applies an appointed direct current voltage to a motor, and, at the same time, the difference between the target position and the present position is controlled to become zero by a sensor for detecting the motor position.
However, in the related art motor-controlling circuit, there are some problems. One problem is a difficulty in guaranteeing smooth rotation control of the motor and accurate reappearance of the stopping position thereof at high precision. Another problem is an increase in costs of semiconductor elements because the loss of the corresponding semiconductor elements is increased when applying power voltage to the motor using semiconductor switching elements such as transistors, and some heat radiation devices are required. Therefore, heretofore it has been very difficult to achieve accurate and stable operations with respect to all the running environments of a vehicle, and difficult to suppress an increase in costs.
The present invention relates to a motor-controlling circuit, for the optical-axis-adjusting unit of a vehicle illuminating device, which motor-controlling circuit guarantees smooth rotation control of a motor that is used as a drive source for adjusting the optical axis, and guarantees accurate repetition of the motor-stopping position, but does not require a remarkable increase in cost.
In order to achieve the above problems, the invention is featured in that a motor-controlling circuit, for an optical-axis-adjusting unit of a vehicle illuminating device, having a direct current motor as a drive source for adjusting the optical axis and a position detecting portion thereof, which carries out feedback control so that an error value between the present position information of the motor, which is obtained by the position detecting portion, and a target value of position control becomes zero, comprises:
a proportional calculation portion for calculating said error;
an integration calculation portion for integrating the errors calculated by said proportional calculation portion;
a differential calculation portion for calculating a first-order derivative per time with respect to the position information from said position detecting portion;
a PID calculation processing portion for calculating an amount of control by adding respective outputs of said proportional calculation portion, the integration calculation portion, and the differential calculation portion, after the respective outputs have been multiplied by respective weighting coefficients; and
a pulse width modulating (PWM) control portion for generating a control signal having a duty cycle that is varied in response to the amount of control from said PID calculation processing portion, and for carrying out drive control of the direct current motor on the basis of said control signal.
Therefore, according to the present invention, since motor control is carried out on the basis of a pulse width modulation signal responsive to the amount of control by the PID calculation processing portion, it is possible to guarantee both smooth rotation control of a motorxe2x80x94which is a drive source for adjusting the optical axisxe2x80x94and accurate repetition of the motor-stopping position, whereby it is possible to achieve a decrease in the switching loss and to prevent the cost thereof from increasing.